DFFF

1. S
SUVITHA E V
HSST Chemistry
GHSS Koduvayur, Palakkad

3. 3
Starting materials for the synthesis of wide range of organic compounds.
Chlorine containing antibiotic, chloramphenicol, produced by
microorganisms is very effective for the treatment of typhoid fever.
Thyroxine Our body produces iodine containing hormone, , the deficiency of
which causes a disease called goiter.
Chloroquine Synthetic halogen compounds
, viz. is used for the treatment of malaria;
halothane is used as an anaesthetic during surgery.
Certain fully fluorinated compounds are being considered as potential blood
substitutes in surgery.

4. 4
Replacement of hydrogen atom in an aliphatic or aromatic hydrocarbon by
halogen atom
halogen atom(s) attached
to the sp 3
hybridised carbon
atom of an alkyl group
halogen atom(s) attached
to sp 2
hybridised carbon
atom(s) of an aryl group.
Haloalkane
Alkyl halide (haloalkane)
Haloarene
Arylhalide (haloarene)
Haloalkanes Haloarenes
Alkane Arene
Halo+alkane Halo +arene

5. 5
The replacement of hydrogen atom(s) in an aliphatic
or aromatic hydrocarbon
by halogen atom
Halogen atom(s) attached to the sp 3
hybridised carbon atom of an alkyl group
Aryl halide (haloarene)
Alkyl halide(haloalkane)
Halogen atom(s) attached to sp 2
hybridised
carbon atom(s) of an aryl group.

6. 6

7. 7
10.1.2 Compounds Containing sp 3
C—X Bond (X= F, Cl, Br, I)
Halogen is attached to
primary Carbon atom
Halogen is attached to
secondary carbon atom
Halogen is attached to
tertiary carbon atom
(a) Alkyl halides or haloalkanes (R—X)

9. 9
(b) Allylic halides
Halogen atom is bonded to an sp 3
-hybridised carbon atom adjacent to carbon-carbon
double bond (C=C) i.e. to an allylic carbon.
(c) Benzylic halides
Halogen atom is bonded to an sp 3
-hybridised carbon atom attached to an aromatic ring.

10. 10
10.1.3 Compounds Containing sp 2
C—X Bond
(a) Vinylic halides
(b) Aryl halides
Halogen atom is bonded to a sp 2
-hybridised carbon atom of a carbon-carbon double
bond (C = C).
Halogen atom is directly bonded to the sp 2
-hybridised carbon atom of an aromatic ring.

11. 11 / 76
●
Common names the alkyl group followed by the name of halide.
●
IUPAC system halosubstituted hydrocarbons.
●
Common & IUPAC names are the same For mono halogen substituted
derivatives of benzene( for Haloarenes)
●
Common system For dihalogen derivatives, the prefixes o-, m-, p- are used
●
IUPAC system the numerals 1,2; 1,3 and 1,4 are used.

12. 12 / 76

13. 13
The dihaloalkanes having the same type of halogen atoms are named as
alkylidene or alkylene dihalides.
when both the halogen atoms are present on
the same carbon atom of the chain
when halogen atom are present on
adjacent carbon atoms.
Geminal halides or gem-dihalides Vicinal halides or vic-dihalides

14. 14

15. 15
Halogen atoms are more
electronegative than carbon
Fluorine
iodine
Carbon-halogen bond length increases
from C—F to C—I.

16. 16
Focus Area

17. 17
Two gaseous products are escapable,
Reaction gives pure alkyl halides
Thionyl chloride
Focus area

18. 18

19. 19
(I) From alkanes by free radical halogenation
a complex mixture of isomeric mono- and polyhaloalkanes,

20. 20
(i) Addition of hydrogen halides:
(ii) Addition of halogens:
As per Markovnikov’s rule.
Discharge of reddish brown colour of bromine
An important method for the detection of double bond in a molecule.

21. 10.4.3 Halogen Exchange
in dry acetone.
Finkelstein reaction.
synthesis of alkyl fluorides
Swarts reaction.
Focus Area

22. 10.6 Physical Properties colourless when pure.
develop colour when exposed to light
Many volatile halogen compounds have sweet smell.
Boiling points of chlorides, bromides and iodides are considerably
higher
●
Molecules of organic halogen compounds are generally polar.
●
Due to greater polarity as well as higher molecular mass as compared to the parent
hydrocarbon, the intermolecular forces of attraction
(dipole-dipole and van der Waals)are stronger in the halogen derivatives.

23. Melting and boiling points
For the same alkyl group, the boiling points of alkyl halides decrease in the
order: RI> RBr> RCl> RF.
This is because with the increase in size and mass of halogen atom, the
magnitude of van der Waal forces increases.

24. The boiling points of isomeric haloalkanes decrease with increase in branching
It is due to symmetry of para-isomers that fits in
crystal lattice better as compared to ortho- and meta-isomers.
I

25. Density
Bromo, iodo and polychloro derivatives of hydrocarbons are heavier than water.
The density increases with increase in number of carbon atoms,
halogen atoms and atomic mass of the halogen atoms

26. Solubility
The haloalkanes are very slightly soluble in water.
Dissolve haloalkane in water.................,.,
energy is required to overcome the attractions between
the haloalkane molecules and break the hydrogen bonds between water
molecules.
Less energy is released ----> when new attractions are set up
between the haloalkane and the water molecules as these are not as
strong as the original hydrogen bonds in water.
As a result, the solubility of haloalkanes in water
Haloalkanes tend to dissolve in organic solvents
the new intermolecular attractions between haloalkanes and
solvent molecules these are very strong in nature

27. 27 / 76
10.7 Chemical Reactions
10.7.1 Reactions of Haloalkanes
Focus Area

28. (1) Nucleophilic substitution reactions
Nucleophiles are electron rich species
Substrate molecule which is electron deficient.
A nucleophile replaces already existing nucleophile in a molecule ---> nucleophilic
substitution reaction.
Halogen atom,
leaving group departs as halide ion.
Substitution reaction is initiated by a nucleophile, ---> nucleophilic
substitution reaction.

29. 29

30. 30
Groups like cyanides and nitrites possess two nucleophilic centres
Ambident nucleophiles
[ C≡N ↔ :C=N ]
Linking through carbon atom
alkyl cyanides
Linking through nitrogen atom
isocyanides.
[ – O— N =O]
Linkage through oxygen
alkyl nitrites
Linkage through nitrogen atom,
nitroalkanes.

31. 31
(a) Substitution nucleophilic bimolecular (S N
2)
Straight line ---> bond in the
plane of the paper.
Solid wedge----> bond
coming out of the paper,
Dashed line --->going down the paper
Incoming hydroxide ion
Outgoing halide ion
Mechanism:

32. carbon-halide bond to break
A new C-O bond formed between
C and -OH(attacking nucleophile).
Incoming nucleophile Alkyl halide
3 C-H bonds
of the substrate
start moving away from the
attacking nucleophile.
no intermediate
In transition state
Attacking nucleophile approaches closer to the carbon,
C-H bonds still keep on moving in the same direction
till the attacking nucleophile attaches to carbon and
leaving group leaves the carbon.

33. 33

34. 34
Configuration is inverted, the same way as an umbrella is turned inside out when
caught in a strong wind.
This process is called as inversion of configuration.
Unstable and cannot be isolated.
carbon is simultaneously bonded to five atoms.
In the transition state,
incoming nucleophile and the outgoing leaving group.
Carbon atom is simultaneously bonded to

35. 35
Tertiary halides
are the least reactive
because bulky groups
hinder the approaching
nucleophiles.
Methyl halides react
most rapidly in S N
2 reactions
because there are only
three small hydrogen atoms

36. 36
(b) Substitution nucleophilic unimolecular (S N
1)
S N
1 reactions are generally carried out in polar protic solvents
(like water, alcohol, acetic acid, etc.).
i.e., the rate of reaction depends upon the concentration of
only one reactant, which is tert- butyl bromide.
follows the first order kinetics,

37. 37
Carbocation
Polarised C—Br bond
Undergoes
slow cleavage
Bromide ion.
Step 1
●
It is the slowest and reversible.
●
Rate of reaction depends upon the slowest step,
●
Rate of reaction depends only on the concentration of alkyl halide and
not on the concentration of hydroxide ion.

38. 38
Carbocation Nucleophile
Step 2
Greater the stability of carbocation,
Greater will be its ease of formation from alkyl halide
and faster will be the rate of reaction.

39. 39
(b) Substitution nucleophilic unimolecular (S N
1)

40. 40
In case of alkyl halides, 30
alkyl halides undergo S N
1 reaction very fast because of the high
stability of 30
carbocations.
Relative Stability of Haloalkanes Towards SN
1 &SN
2 reactions
Presence of bulky group on the carbon containing the leaving group
tends to hinder the approach of nucleophile & slow down the reaction
Methyl > 1 o
> 2 o
> 3 o
3 o
> 2 o
> 1 o
> methyl halide

41. 41
Allylic and benzylic halides show high reactivity towards the S N
1 reaction.
The carbocation thus formed gets stabilised through resonance

42. 42

43. (c) Stereochemical aspects of nucleophilic substitution reactions
Optical activity, chirality, retention, inversion, racemisation
(i) Optical activity:
Optically
active
compounds
●
To the left
●
Anticlockwise Direction
●
laevo-rotatory or the L-form
●
Negative (–) sign is placed
before the degree of rotation.
●
To the right
●
Clockwise direction
●
Dextrorotatory(Greek for right
rotating or d-form
●
Positive (+) sign
before the degree of rotation.
(+) and (–) isomers -->optical isomers
Phenomenon --> optical isomerism.
SN
2---> Inversion /SN
1---> Racemisation

44. 44
(ii) Molecular asymmetry, chirality and enantiomers:
Louis Pasteur
Crystals of certain compounds exist in the form of mirror images
Aqueous solutions of both types of crystals showed optical rotation, equal in magnitude
(for solution of equal concentration) but opposite in direction
This difference in optical activity was associated with the three dimensional
arrangements of atoms in the molecules (configurations) of two types of crystals
Foundation of modern stereochemistry.
Dutch scientist, J. Van’t Hoff and French scientist, C. Le Bel
He demonstrated that
He believed that
The spatial arrangement of four groups (valencies)around a central carbon is
tetrahedral and if all the substituents attached to that carbon are different, the
mirror image of the molecule is not superimposed (overlapped) on the molecule such
a carbon is called asymmetric carbon or stereocentre.
The asymmetry of the molecule along with non superimposability of mirror images is
responsible for the optical activity in such organic compounds.

45. 45
Causes of Optical Activity:
Optical active compounds.............. compounds are chiral .
A molecule is said to be chiral its mirror images are non super impossable
if all the substituents attached
to that carbon are different,
the mirror image of the molecule
is not superimposed (overlapped) on the molecule;
carbon is called asymmetric carbon or stereocentre.
The asymmetry of the molecule along with non superimposability of mirror
images is responsible for the optical activity

46. 46
A molecule contains one asymmetric carbon atom it is always chiral & the
compound shows optical isomerism
Chiral molecules
are optically active,
Achiral molecules
are optically inactive.

47. 47
Propan-2-ol is an achiral molecule.
Butan-2-ol is a Chiral Molecule

48. 48
Four valencies are
satisfied by four different
atoms or groups

49. 49
Enantiomers
Optical isomers are non superimposable mirror images of each other and which rotate
the plane of polarised light equally but in opposite direction

50. 50
A mixture containing two enantiomers in equal proportions
will have zero optical rotation, as the rotation due to one
isomer will be cancelled by the rotation due to the other
isomer.
Racemic Mixture:
----> ( ) ,
A racemic mixture dl or ± before the name
( ) -2- .
for example ± butan ol
:
Racemisation C .
onversion of enantiomer into a racemic mixture

51. 51 / 76
(iii) Retention:
Preservation of the spatial arrangement of bonds to an asymmetric centre during a
chemical reaction or transformation.
No bond to the stereocentre is broken,
Product will have the same general configuration
but the sign of optical rotation has changed in the product

52. 52 / 76
(iv) Inversion, retention and racemisation:
There are three outcomes for a reaction at an asymmetric carbon atom,
when a bond directly linked to an asymmetric carbon atom is broken.
Retention of configuration
Inversion of configuration.
50:50 mixture of A and B is obtained then the process is called
racemisation and the product is optically inactive,

53. 53
Because the nucleophile attaches itself on the side opposite to the one where the
halogen atom is present.
(–)-2-bromooctane (+)-octan-2-ol
SN
2
Optically active alkyl halides
inverted configuration
as compared to the reactant.

54. 54
Carbocation formed in the slow step being sp hybridised is planar (achiral).
Optically active alkyl halides, SN
1 Racemisation
2-bromobutane,
The attack of the nucleophile may be accomplished from either side
of the plane of carbocation resulting in a mixture of products,
one having the same configuration
(the –OH attaching on the
same position as halide ion)
Other having opposite configuration
(the –OH attaching on the side
opposite to halide ion).

55. 55 / 76
A haloalkane with β-hydrogen atom is heated with alcoholic solution of potassium
hydroxide, there is elimination of hydrogen atom from β-carbon and a halogen atom
from the α-carbon atom
2. Elimination reactions

56. 56 / 76
Due to the availability of more than one β-hydrogen atoms,
possibility of formation of more than one alkene
By Russian chemist, Alexander Zaitsev (also pronounced as Saytzeff
“in dehydrohalogenation reactions, the preferred product is that alkene
which has the greater number of alkyl groups attached to the doubly bonded
carbon atoms.”
Saytzeff Rule

57. 57
3. Reaction with metals ----> organo-metallic compounds
Discovered by Victor Grignard
Alkyl magnesium halide, RMgX, referred as
Grignard Reagents.
Grignard reagents are highly reactive
in dry ether.

58. 58
Wurtz reaction
Wurtz-Fittig reaction
Fittig reaction

59. 59
(i) From hydrocarbons by electrophilic substitution
Aryl chlorides and bromides can be easily prepared
The ortho and para isomers can be easily separated
Large difference in their melting points.
Reactions with iodine are reversible in nature and require the presence of an oxidising
agent (HNO 3
, HIO 4
) to oxidise the HI formed during iodination.
Fluoro compounds are not prepared by this method due to high reactivity of fluorine.
10.5 Preparation of Haloarenes

60. 60
(ii) From amines by Sandmeyer’s reaction
Focus Area

61. 61

62. 62
10.7.2 Reactions of Haloarenes
1. Nucleophilic substitution
Aryl halides are extremely less reactive towards nucleophilic substitution
reactions due to the following reasons:
(i) Resonance effect
(ii) Difference in hybridisation of carbon atom in C—X bond
(iii) Instability of phenyl cation:
(iv) Because of the possible repulsion, it is less likely for the
electron rich nucleophile to approach electron rich arenes

63. 63
(i) Resonance effect :
In haloarenes, the electron pairs on halogen atom are in conjugation with
π-electrons of the ring and the following resonating structures are possible.
The bond cleavage in haloarene is difficult than haloalkane
, they are less reactive towards nucleophilic substitution reaction.
C—Cl bond acquires a partial double bond Due to resonance.

64. 64
(ii) Difference in hybridisation of carbon atom in C—X bond:
The sp 2
hybridised carbon with a greater s-character is more electronegative and can
hold the electron pair of C—X bond more tightly than
therefore, haloarenes are less reactive than haloalkanes
towards nucleophilic substitution reaction.
sp 3
-hybridised carbon in haloalkane with less s-chararcter.
C—Cl bond length in haloalkane is 177pm
in haloarene is 169 pm
Difficult to break a shorter
bond than a longer bond,

65. 65
(iii) Instability of phenyl cation:
In case of haloarenes, the phenyl cation formed as a result of self-ionisation
will not be stabilised by resonance and therefore, S N 1 mechanism is ruled
out.
(iv) Because of the possible repulsion, it is less likely for the electron
rich nucleophile to approach electron rich arenes.

66. 66
Replacement by hydroxyl group

67. 67
Can you think why does NO 2 group show its effect only at ortho- and para- positions
and not at meta- position?
As shown, the presence of nitro group at ortho- and para-positions withdraws the
electron density from the benzene ring and thus facilitates the attack of the
nucleophile on haloarene.
The carbanion thus formed is stabilised through resonance.
The negative charge appeared at ortho- and para- positions with respect to the
halogen substituent is stabilised by –NO 2
group while in case of meta-nitrobenzene,
none of the resonating structures bear the negative charge on carbon atom bearing
the –NO 2
group.
Therefore,the presence of nitro group at meta- position does not stabilise the
negative charge and no effect on reactivity is observed by the presence of –NO 2
group at meta-position.

68. 68
2. Electrophilic substitution reactions
Haloarenes undergo the usual electrophilic reactions of the benzene ring
such as Halogenation,
Nitration,
Sulphonation
Friedel-Crafts reactions.
Substitution occurs at ortho- and para-positions with respect to the halogen atom.
Due to resonance, the electron density
increases more at ortho- and
para-positions than at meta-positions.
●
the ring deactivated as compared to benzene
●
the electrophilic substitution reactions
in haloarenes occur slowly and
require more drastic conditions as
compared to those in benzene.
The halogen atom because
of its –I effect has some
tendency to withdraw electrons
from the benzene ring.
As a result,
Focus Area

69. 69
2. Electrophilic substitution reactions

70. 70

71. 71
3. Reaction with metals

72. 72
10.7 Polyhalogen Compounds
10.7.1 Dichloro-methane(Methylenechloride)
10.7.2 Trichloro-methane(Chloroform)
10.7.3 Triiodo-methane(Iodoform)
10.7.4 Tetrachloromethane(Carbontetrachloride)
10.7.5 Freons
10.7.6 Dichlo-rodiphenyl-trichloro-ethane(DDT)

73. 73
●
Paint remover,
●
Propellant in aerosols,
●
Solvent in the manufacture of drugs.
●
Metal cleaning and finishing solvent
●
Solvent for fats, alkaloids,Iodine
●
Production of the freon refrigerant R-22.
●
anaesthetic in surgery
Dichloro-methane
(Methylenechloride)
Trichloro-methane
(Chloroform)
poisonous gas, carbonyl chloride, also known as
phosgene
It is therefore stored in closed dark coloured
Bottles completely filled so that air is kept out.

74. 74
●
Triiodo-methane
(Iodoform)
Tetrachloromethane
(Carbontetrachloride)
Antiseptic
●
Manufacture of refrigerants and propellants
for aerosol cans
●
synthesis of chlorofluorocarbons
and other chemicals
●
cleaning fluid, both in industry as a degreasing
agent, and in the home, as a spot remover and as
fire extinguisher.,
●
pharmaceutical manufacturing, and general
solvent

75. 75
●
Chlorofluorocarbon compounds
of methane and ethane
●
Aerosol propellants, refrigeration
and air conditioning purposes
first chlorinated organic insecticides
Freons Dichlo-rodiphenyl-trichloro-
ethane(DDT)

76. 76
Thank You